The present invention relates to a laminated polyester film and more particularly, it relates to a laminated polyester film comprising a polyester layer containing a sufficient amount of fine cells and at least one other polyester layer containing substantially no fine cells (hereinafter referred to merely as "laminated polyester film") which has a reduced weight per unit volume and a good cushioning property, image-receiving papers suitable for a laser printer, a color printer and a video printer, and a mount suitable for seal print, which papers and mount are composed of the laminated polyester film.
Biaxially-oriented polyester films have widely used as industrial materials because they can exhibit well-balanced various properties or characteristics and are excellent in cost performance. Further, fine cell-containing polyester films which are produced as light-weight white opaque films having a good cushioning property by blending a polyester with a thermoplastic resin immiscible therewith and molding the resultant blend into a film shape, have been applied, for example, to synthetic papers such as image-receiving papers for a laser printer, a color printer or a video printer, or mounts for seal print, a base film of magnetic cards or the like. Especially, in the case where these films are used as the image-receiving papers, for enhancing a definition of images formed thereon, white pigments and/or fluorescent whitening agents are blended in the films so as to increase a yellowness thereof.
Also, the fine cell-containing polyester films have been applied to mounts (release backing paper) onto which an image-printed seal is attached, due to a high cushioning property thereof. For instance, the mounts have been used for a photo seal prepared by such an amusement apparatus in which a favorable frame configuration or background is first selected and then a photograph of a person or persons posed in front thereof is taken by an instant camera, so that many photo seals can be instantaneously produced.
In order to reduce the production cost of such white opaque films, it is required to use white pigments or fluorescent whitening agents effectively.
Further, as is well known in the art, when the fine cell-containing polyester films are used as a mount of image-receiving papers or printing papers, surface conditions thereof give a considerable influence on an quality of images printed thereon. Specifically, in the case where the film has a rough surface due to the waviness of fine cells present in close proximity to the surface, the definition of images printed thereon becomes deteriorated, so that there is caused such an inconvenience that no clear and fine images cannot be obtained.
Furthermore, when the fine cell-containing polyester film is produced, there arises such a problem that a cast roll, a stretching roll and the like are soiled by the immiscible thermoplastic resin present in close proximity to the surface of the film.
As a result of various studies by the present inventors, it has been found that, by laminating another specific polyester layer on at least one of surfaces of the base polyester film containing immiscible thermoplastic resin in a specified range, the obtained laminated polyester film exhibit a reduced weight per unit volume and good cushioning property. The present invention has been attained on the basis of the finding.